Abstract

Background

In a previous study of 222 patients we showed how epigenetic and genetic changes during oncogenic progression could possibly explain the adenoma- carcinoma sequence: first, methylation of promoters of H-cadherin gene followed by MGMT methylation, K-ras oncogene G to A point mutations, activation of B-raf gene by a V600E mutation finally methylation of E-cadherin. (ASCO 2011, abstr.3608) We extended the study by examining PTEN, PIK exon 9 and 20 for mutations and methylation and correlated all the genes to tumor stage. We divided TNM into early stage I & II and late III & IV.

Method

Ethical approval was obtained. DNA was extracted from tumor samples obtained from CRC patients by resection. The PTEN methylation was analyzed by methylation-specific PCR. and analyzed by gel electrophoresis after Sybr green staining and UV-photography.

Results

Data were available for 117 patients. Correlation coefficients were calculated and their significance assessed using Chi-squared: RAS/BRAF either mutant (mut) with late stage, P = 0.123 (suggestive), RAS/BRAF either mut with MGMT methylated, P = 0.017 (significant); PIK mut with PTEN methylated, P = 0.044 (significant); and PIK mut with CDH13 methylated, P = 0.123 (suggestive). Concerning RAS/BRAF and stage, 86% of RAS/BRAF either mut tumours, were late stage, while only 53% of wild type (wt) tumors were late stage. For RAS/BRAF and MGMT, 76% of RAS/BRAF either mut were MGMT methylated, but 53% of wt tumors were methylated. PIK mut tumors were also PTEN methylated, and CDH13 methylated. Results are tumor specific as all blood controls were unmethylated resp. wt.

Conclusion

With PIK, PTEN and CDH13 no significant correlation was noted with either MGMT unmethylated or methylated nor with RAS/BRAF either wt or mut. RAS/BRAF correlated significantly with MGMT (p = 0.017), methylated PIK, PTEN and CDH13 did not correlate with early or late stage. There was a tendency, of RAS/BRAF mut to be associated with late stage. Of all these markers none correlates in a significant fashion with early or late stages and as of now, despite multiple genetic and epigenetic data sets, no predictive statement can be made.